A detection device of the above-described type has become known from DE-C 27 31 361. The detection device is connected to a pressurized gas container or a pressurized gas line via a coupling. Besides the coupling, it contains a pressure reducer, a shut-off valve interrupting the sampling flow, a flow meter for measuring the sampling flow, and a gas detector tube arranged downstream of the flow meter. To carry out a gas analysis, a predetermined gas sample volume is passed through the gas detector tube, and the percentage of the component to be detected in the pressurized gas is determined on the basis of the change in the color of the reaction layer of the gas detector tube.
The disadvantage of the prior-art device is that a separate time-keeping device, which is often not at hand in routine operation, is necessary to set the volume of the gas sample. Since the user also must manually determine the gas sampling interval with the time-keeping device, deviations in the gas sample volume to be set from the actually occurring gas sample volume cannot be ruled out, and the concentration value read on the gas detector tube will be inaccurate.
A device for measuring certain components in air or other gases has become known from DE-PS 10 93 113, in which individual detector tubes are exposed to a predetermined gas sample volume by means of a control ensured by a timer by the detector tubes being connected to the gas sampling flow by a rack-and-pinion gear controlled by the timer. The prior-art device is designed for the long-term monitoring of gas concentrations, e.g., in work rooms, without an operator having to be involved in the measurement.